This invention relates generally to package wrapping machines utilizing thin, stretchable film to wrap and display articles contained in trays and, more particularly, to the detection of jams within such machines and the removal of such jams once they have occurred.
A variety of wrapping machines are available in the prior art to provide for wrapping packages with sections of thin, stretchable film by means of various mechanical techniques which wrap the film about the package and then seal the film. To accomplish the wrapping, the packages are typically passed through the machine by a variety of conveyors and/or elevators. During the passage through the wrapping machine, it is possible that various package pushers or film folding apparatus may become jammed with the package that is being wrapped. Due to the fact that wrapping machines are typically large and driven by powerful motors, jam conditions can damage various parts of the machine as well as present difficult and time consuming removal operations for the machine operator.
Known prior art stretch film wrapping machines rely on the slippage of drive belts, torque limiters, mechanical lever assemblies or the like to deal with jam conditions. For example, a mechanical system is disclosed in U.S. Pat. No. 4,134,246. In the jam detection system of the cited patent, a drive mechanism includes a swing arm and a pivotal sub-arm which are interconnected so that the sub-arm tends to separate from the swing arm if a jam occurs. As the sub-arm separates from the swing arm, a switch is opened to de-energize the wrapping machine drive motor.
While such jam detection or alleviation techniques are generally reliable, they can require periodic adjustments, maintenance and/or additional mechanical apparatus. For example, if belts are not maintained in proper condition and adjustment, a slipping belt arrangement may not adequately protect the machine. This can also be true with a torque limiter. Of course, the additional adjustments and/or mechanical apparatus required can make such systems less reliable and more expensive. Furthermore, in known prior art wrapping machines, no provisions are made to facilitate the removal of a jam condition once it has occurred.
It is, thus, apparent that the need exists for an improved system for not only detecting jams which may occur within a film wrapping machine, but also for facilitating the removal of such jams if they do occur.